Light coming from a light emitting diode (LED) source is managed and modified using lenses using refraction and total internal reflection (TIR). These lenses have to be mounted over the LED, while still maintaining a distance of the LED and the lens as per an optical design. One of the ways to mount the LED is by attaching a base to the lens, which is then attached to the LED.
The base of the lens is manufactured with a certain thickness. If the thickness of the base is greater than the thickness of the base of the LED, then the base is attached higher with respect to the lens. This changes the optical design, since a portion of the base of the lens is in the optical path of the light rays emitted from the LED. The light instead of being totally internally reflected in this area, leaks out of the side of the lens through the base. This impacts both a viewing angle and a uniformity of the light beam.